CALIFORNIA 
AGRICULTURAL  EXTENSION  SERVICE 


CIRCULAR     16 

APRIL,  1928 


IRRIGATION  OF  ORCHARDS 
BY  CONTOUR  FURROWS 

M.  R.  HUBERTY  AND  J.  B.  BROWN 


PUBLISHED  BY 

THE  COLLEGE  OF  AGRICULTURE 
UNIVERSITY  OF  CALIFORNIA 


Cooperative  Extension  work  in  Agriculture  and  Home  Economics,  College  of  Agriculture, 
University  of  California,  and  United  States  Department  of  Agriculture  cooperating.  Dis- 
tributed in  furtherance  of  the  Acts  of  Congress  of  May  8  and  June  30,  1914.  R.  H.  Crocheron, 
Director,  California  Agricultural  Extension  Service. 


UNIVERSITY  OF  CALIFORNIA  PRINTING  OFFICE 

BERKELEY,   CALIFORNIA 

1928 


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IRRIGATION  OF  ORCHARDS  BY  CONTOUR  FURROWS1 

M.  E.  HUBERTY2  and  J.  B.  BKOWNs 


INTRODUCTION 

During  the  past  few  years  there  has  been  a  considerable  increase 
in  the  development  of  hillside  orchard  planting.  This  development 
has  come  about  through  the  recognition  of  the  favorable  situation  of 
the  foothills  from  the  standpoint  of  frost  hazard.  Furthermore,  many 
of  the  newer  irrigation  projects  are  located  in  the  foothill  areas  where 
orchard  management  operations  can  not  be  carried  on  in  the  same 
manner  as  in  the  flat  valley  areas. 

Contour  planting,  or  the  establishment  of  tree  rows  along  grade 
contours  of  little  slope,  is  one  of  the  means  used  to  irrigate  hillside 
orchards  more  effectively.  This  system  of  orchard  layout  is  adaptable 
to  rolling  topography  where  the  cost  of  leveling  would  be  excessive, 
and  is  particularly  adapted  to  shallow  soils  where  any  considerable 
movement  of  the  surface  soil  in  leveling  operations  would  expose  bed- 
rock or  subsoil  poorly  adapted  to  tree  growth. 


TYPES    OF    CONTOUR    PLANTING 

In  general  there  are  three  types  or  classes  of  contour  layouts,  as 
follows: 

1.  Uniform  spacing  of  trees  along  a  grade  contour  without  regard 
to  alignment. 

2.  Uneven  spacing  of  trees  along  grade  contour  with  straight 
crossrows. 

3.  Trees  planted  on  varying  grades  with  straight  crossrows. 
The  three  types  are  illustrated  in  figures  1,  2  and  3. 

When  the  trees  of  an  orchard  are  planted  as  in  type  1,  they 
usually  do  not  form  smooth  curves  along  the  contour  nor  are  the 
crossrows  straight.  This  method  provides  uniform  grade  in  the  fur- 
rows and  reasonably  uniform  spacing  of  trees.  The  trees  however, 
not  being  in  straight  crossrows,  hinder  cross  cultivation  and  increase 


1  The  information  presented  in  this  publication  has  been  obtained  by  the 
Division  of  Irrigation  Investigations  and  Practice  and  the  Agricultural  Extension 
Service  largely  from  designers,  owners  and  operators  of  contour  orchards.  In 
addition  to  the  authors,  Frank  Davis,  Junior  Irrigation  Engineer,  Division  of 
Irrigation  Investigations  and  Practice,  participated  in  the  field  work. 

2  Assistant  Irrigation  Engineer  in  the  Experiment  Station. 

3  Extension  Specialist  in  Irrigation. 


CALIFORNIA    AGRICULTURAL    EXTENSION    SERVICE  [ClRC.  16 


the  difficulty  of  detecting  broken  furrows  which  often  occur  in  con- 
tour irrigation.  As  cultivation  is  generally  in  one  direction  only 
orchards  planted  in  this  manner  eventually  become  terraced.  This 
method  is  used  when  the  planting  is  on  steep,  irregular  topography. 


Fig.  1. — Uniform  spacing  of  trees  along  grade  contours;  crossrows  not  straight. 


O o 

Fig.  2. — Uneven  spacing  of  trees  along  grade  contour;  crossrows  straight. 


Fig.  3. — Trees  planted  on  varying  grades ;   crossrows  straight.     Tree  rows 
along  the  contour  form  smoother  curves  than  in  types  1  and  2. 


1928 


IRRIGATION    OF    ORCHARDS    BY    CONTOUR    FURROWS 


Type  2  differs  from  type  1  in  that  the  crossrows  are  straight.  On 
long,  even  slopes  the  crossrows  can  be  placed  parallel,  or  nearly  so, 
while  on  knolls  they  are  usually  placed  radially  as  there  are  more 
trees  to  the  tree  row  at  the  base  of  the  hill  than  there  are  at  the  top. 
This  type  of  planting  provides  uniform  grade  and  allows  for  cross 
cultivation,  but  at  times  it  may  result  in  a  fewer  number  of  trees  per 
acre  than  with  the  first  method.  If  cultivation  in  two  directions  is 
practiced,  the  possibility  of  forming  terraces  is  lessened.  In  type  3 
trees  are  planted  on  varying  grades  and  in  straight  crossrows.     This 


Fig.  4. — Distribution  of  water  from  flume. 

provides  a  smooth  curve  along  the  tree  row  and  is  an  advantage  in 
cultivating,  but  unless  care  is  used,  loss  of  grade  may  result  from 
moving  the  trees  too  far  transversely  to  the  grade  contour.  This 
method  can  be  used  where  the  cross  slope  is  not  too  steep  and  where 
the  grade  in  the  contour  row  is  sufficient  (1%  to  3  feet  in  100  feet) 
to  allow  for  a  variance  of  grade. 


THE   WATER    DISTRIBUTION    SYSTEM 

In  the  distribution  of  water  to  a  contour  planting  it  is  necessary 
to  have  the  water  under  control  at  all  times.  For  this  reason  pipes 
or  flumes  are  usually  employed.  In  general,  flumes  (fig.  4)  are  in 
the  way  of  cultural  operations,  but  there  is  an  advantage  in  their 
favor  in    that  water  can   readily  be   delivered   from  them  through 


6  CALIFORNIA    AGRICULTURAL    EXTENSION    SERVICE  [OlRC.  16 

numerous  openings  into  the  furrows,  thus  lessening  the  tendency  of 
too  much  water  collecting*  in  one  furrow.  The  objection  to  the  use 
of  flumes  is  largely  overcome  when  they  are  placed  only  along  the 
edge  of  the  fields. 


Contour  furrows 

tfydronts 


Overflow 
sfond 


Fig.  5. — Types  of  concrete  pipe  distributing  devices. 

Pipes  of  iron,  wood,  burned  clay  and  concrete  are  used  in  the 
distribution  of  water  to  contour  plantings.  When  iron  or  wood  pipe 
is  used  the  common  method  of  delivering  water  from  the  pipe  line  to 
the  tree  row  is  by  means  of  a  garden  hydrant,  but  when  burned  clay 
or  concrete  pipe  is  used  an  orchard  hydrant,  or  some  overflow  device, 
such  as  shown  in  the  lower  right-hand  corner  of  figure  5,  is  usually 
employed.  This  type  of  hydrant  allows  water  to  be  removed  and 
excess  water  to  by-pass  back  into  the  pipe  line. 


1928J 


IRRIGATION    OF    ORCHARDS    BY    CONTOUR   FURROWS 


The  distributing-  hydrants  are  usually  placed  far  enough  above 
the  tree  rows  so  that  one  furrow  can  be  led  from  the  hydrant  to  the 
upper  side  of  the  row.  The  number  of  spouts  on  the  hydrant  varies, 
but  four  represents  common  practice  for  contour  plantings.  Where 
more  than  one  furrow  to  the  tree  row  is  being  used  some  irrigators 
prefer  to  attach  a  portable  distributing  device  to  the  hydrant.  This 
device  may  be  made  in  the  form  of  a  pipe  or  flume  with  openings 
spaced  the  distance  between  furrows, 


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Fig.  6. 
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— Desirable  grades  for  contour  planting.  The  horizontal  divisions  on 
represent  the  slope  of  the  land  at  right  angles  to  the  contour  row, 
vertical  scale  represents   desirable  grade  of  tree  row. 


GRADE   OF   CONTOUR   ROWS 

The  grades  upon  which  the  contour  rows  are  placed  depends 
largely  upon  the  soil  type  and  the  amount  of  cross  slope.  The  general 
tendency  in  the  early  development  of  contour  layouts  was  to  use 
grades  that  were  too  flat.  Heavy  soils  take  water  slowly  but  they 
can  withstand  high  velocities  while  light  soils  absorb  water  easily  and 
wash  readily.  In  any  event  the  water  must  be  so  controlled  that  the 
quantities  run  in  the  furrows  can  be  carefully  regulated.  Figure  6 
represents  desirable  grades  for  the  various  soil  types,  For  an  orchard 
planted  on  medium  soil  where  the  cross  slope  of  the  land  is  only  4  feet 
to  100  feet,  a  grade  as  flat  as  1  foot  to  100  feet  might  be  used.  As 
the  cross  slope  of  the  land  increases  the  grade  of  the  furrow  should 
increase,  so  that  on  cross  slopes  of  20  to  25  feet  to  100  feet  a  grade  of 


8 


CALIFORNIA    AGRICULTURAL    EXTENSION    SERVICE  [OlEC.  16 


2  feet  in  100  feet  would  be  advisable.  The  table  should  not  be  inter- 
preted too  rigidly.  It  is  meant  to  show  within  what  limits  it  is 
desirable  to  work,  and  that  the  steeper  grade  of  furrow  is  used  with 
the  steeper  cross  slopes. 

It  is  desirable  that  no  grade  flatter  than  1  foot  in  100  feet  be  used. 
This  will  permit  small  deviations  in  the  direction  of  the  furrow  and 
still  give  enough  slope  for  water  to  flow  freely.  Also  there  is  a 
tendency  in  time  for  shallow  swale-like  depressions  to  appear  midway 
between  crossrows  and  if  the  grade  is  too  slight  the  water  will  tend 
to  break  out  of  the  furrow  at  these  places. 


Fig.  7. — A  pipe  line  placed  down  the  average  slope  of  a  knoll  as  shown  in  the 
distance  in  the  picture,  and  at  the  right  in  the  foreground,  allows  water  to  be 
taken  from  it  on  both  sides. 

The  heavy  adobe  soils  in  the  citrus  areas  that  are  subject  to 
" cracking"  present  a  special  case.  If  contouring  is  to  be  done  on 
this  type  of  soil  the  grades  of  the  tree  rows  will  have  to  be  materially 
increased  in  order  to  overcome  the  tendency  of  the  water  to  leave  the 
furrow  through  the  transverse  soil  cracks. 


METHODS   OF    LAYOUT 


A  contour  map  of  the  area  to  be  planted,  while  not  absolutely 
necessary,  will  always  prove  helpful  in  determining  the  general  plan 
of  layout.  In  no  case  should  one  try  to  place  the  tree  locations  on 
the  map  and  then  expect  to  be  able  to  go  into  the  field  and  fix  them 


1928] 


IRRIGATION    OF    ORCHARDS    BY    CONTOUR    FURROWS 


accordingly ;  tree  location  must  be  done  in  the  field.  As  a  rule  the 
furrows  will  range  in  length  from  300  to  600  feet,  with  the  longer 
furrows  being  used  on  the  heavier  soils.     The  location  of  the  water 


distribution  system  will  be  governed  by  the  size  and  shape  of  tract,  by 
the  location  of  roads  and  natural  drains  and  by  the  length  of  furrow 
runs.  On  small  tracts  the  distributing  lines  may  be  run  along  a 
border,  but  in  larger  areas  they  may  be  placed  down  a  ridge  or  across 
the  average  slope   (figs.  7  and  8). 


10 


CALIFORNIA    AGRICULTURAL    EXTENSION    SERVICE  [ClRC.  16 


In  figure  7  the  pipe  line  is  placed  down  the  ridge.  This  allows 
water  to  be  taken  from  the  pipe  in  both  directions.  Run-off  from  the 
ends  of  the  furrows  can  be  discharged  into  natural  channels  and 
depressions.  However,  unless  the  run-off  from  the  furrows  is  held 
down  to  very  small  quantities  it  is  not  safe  to  discharge  it  into  a 
natural  depression  in  the  orchard  unless  an  artificial  drain  flume  is 
placed  there.  Figure  8  represents  a  long,  even  slope  with  the  dis- 
tributing lines  placed  approximately  parallel.  The  run-off  irrigation 
water  from  tract  A  passes  directly  into  tract  B.  If  the  amount  of 
waste  water  at  the  lower  end  of  furrows  is  carefully  regulated  it  is 
possible  to  continue  these  furrows  a  short  distance  into  the  next  block. 


LAYING    OUT   THE    SYSTEM    IN    THE    FIELD 

When  a  general  plan  of  layout  has  been  decided  upon,  detail  work 
can  be  started.  The  soil  on  side  hills  is  usually  too  shallow  to  allow 
for  much  leveling  so  the  common  practice  is  to  use  a  float  or  a  drag 
to  smooth  the  soil  surface. 


SPIRIT   LEVEL  <i- 


3    EE 

-  L 


K 


\    0 


Fig.  9. — Grade  board  used  in  locating  tree  positions.  The  device  is  usually  made 
the  length  of  the  distance  between  trees,  represented  by  L.  The  short  leg  A  may 
be  any  convenient  height.  The  amount  of  fall  in  the  length  L  is  represented  in 
the  longer  leg  by  C  If  an  adjustable  leg  is  used,  as  shown  at  the  right,  the 
grade  can  be  easily  changed. 


The  tree  locations  may  be  determined  by  the  use  of  a  grade  board 
(fig.  9),  an  engineer's  level,  or  a  hand  level.  Farmers  as  a  rule  prefer 
to  use  the  grade  board  while  engineers  generally  use  the  level  or  hand 
level.  For  the  shorter  distances  of  tree  spacing  the  length  of  the 
grade  board  may  be  made  equal  to  the  distance  between  trees,  but 
for  the  greater  distances  it  is  preferable  to  make  the  length  of  the 
board  one-half  the  distance  of  planting.  When  this  is  the  case  the 
difference  in  length  between  the  grade  board  legs  is  one-half  that 


1928 


IRRIGATION    OF    ORCHARDS    BY    CONTOUR    FURROWS 


11 


listed  in  table  1.  For  the  longer  lengths  it  is  difficult  to  make  a  grade 
board  that  is  light  enough  to  be  easily  handled  yet  rigid  enough  to 
give  accurate  grades. 

Table  1  gives  the  fall  within  the  distance  between  trees  in  the 
rows,  figures  for  distances  ranging  from  18  to  25  feet  and  for  grades 
of  1  to  3  feet  in  100  feet, 

TABLE  l 

Fall  of  Contour  Bow  within  the  Distance  between  Trees 


Grade 
(Feet 

Distance  of  tree  planting  in  feet 

in  100 
feet) 

18 

19 

20 

21 

22 

23 

24 

25 

Ft. 

In. 

Ft. 

In. 

Ft. 

In. 

Ft. 

In. 

Ft. 

In. 

Ft. 

In. 

Ft. 

In. 

Ft. 

In. 

1.0 

0.18 

2?'l6 

0.19 

2M 

0.20 

2Vh 

0.21 

2H 

0.22 

2V% 

0.23 

2% 

0.24 

2% 

0.25 

3 

1.5 

0.27 

3M 

0.28 

3%6 

0.30 

1% 

0.31 

3M 

0.33 

Wit 

0.34 

iVs 

0.36 

4%6 

0.37 

4H 

2.0 

0.36 

4*16 

0.38 

4%6 

0.40 

4>?'l6 

0.42 

5#6 

0.44 

VA 

0.46 

5V2 

0.48 

5% 

0.50 

6 

'   2.5 

0.45 

5% 

0.47 

5H'ie 

0.50 

6 

0.52 

6%6 

0.55 

VA 

0.57 

VA 

0.60 

7?i6 

0.62 

IVi 

3.0 

0.54 

VA 

0.57 

6Hl6 

0.60 

7fw 

0.63 

7Ti6 

0.66 

7^16 

0.69 

m 

0.72 

85A 

0.75 

9 

The  general  procedure  in  laying  out  the  distributing  system  and 
in  staking  out  the  trees  is  the  same  regardless  of  the  type  of  contour 
planting  selected.  Start  by  locating  the  position  of  the  water  distri- 
buting line,  then  establish  the  line  which  is  to  control  the  spacing  of 
the  contour  rows.  This  line,  or  control  row,  is  perpendicular  to  the 
direction  of  the  contour  rows  and  is  the  base  line  used  in  spacing  the 
contour  rows.  It  should  be  located  on  the  average  cross  slope  of  the 
area  planted.  If  the  water  distributing  line  crosses  the  average  slope 
of  the  area  to  be  planted,  then  the  control  row  can  be  established 
parallel  with  and  adjacent  to  it.  If  the  water  lines  are  not  located 
on  the  average  slope,  then  the  tree  rows  must  be  run  in  either  direc- 
tion from  the  control  row.  Mark  the  position  of  the  first  tree  on 
the  control  row,  then  mark  along  the  control  row  the  intervals  at 
which  you  wash  to  space  the  contour  rows.  These  distances  will  not 
necessarily  remain  constant  for  as  the  work  develops  it  may  be  neces- 
sary to  make  a  slight  change  in  spacing  in  order  to  do  away  with 
the  use  of  a  spike  or  stub  row  (fig.  10). 

If  a  grade  board  is  used,  start  by  placing  the  short  leg  of  the 
board  on  the  control  row  at  the  location  of  the  first  tree,  then  carry 
the  other  end  of  the  board  around  until  the  spirit  level  reads  level 
and  mark  with  a  stake  the  position  of  the  longer  leg.  This  work  is 
repeated  until  the  end  of  the  tree  row  is  reached  and  then  a  new 
row  is  started. 


12 


CALIFORNIA    AGRICULTURAL    EXTENSION    SERVICE  [OlRC.  16 


-O o, 

^4=  Stub  row   Sso.^ 

J5  -    /=///    /^av  ~"0 — °—-o^. 

Z>  s  P/'pe   t/ne  /v/th 

control  row  adjacent 


$z**&gntour 


Contour  interna/  A  feet     \       Nt)s 
Trees  e-4  feet  apart 
Orade  1  foot  in  100  feet 


>-o 

Orude  contour 

tv/fh  trees 

Fig.   10. — Kinds  of  tree  rows  found  in  contour  plantings. 


sO. 


As  a  rule  the  rows  will  not  continue  at  a  uniform  distance  apart 
but  will  tend  to  crowd  or  spread,  depending  upon  whether  the  cross 
slope  increases  or  decreases.  This  can  sometimes  be  controlled  by 
changing  the  grade  of  the  tree  row.  A  change  of  grade  will  not 
always  overcome  the  difficulty  and  in  this  case  a  tree  row  must  be 
added  or  dropped,  depending  upon  the  particular  conditions.  For 
trees  planted  on  rows  20  feet  apart  a  minimum  distance  between  rows 
would  be  about  16  feet,  or  a  variation  of  about  20  per  cent  from 
normal.  Should  the  rows  tend  to  come  closer  than  this  the  row  should 
be  stopped,  forming  a  stub  row.    If  the  converse  is  true  and  the  rows 


1928] 


IRRIGATION    OF    ORCHARDS    BY    CONTOUR    FURROWS 


13 


diverge,  a,  new  row  is  started,  as  soon  as  the  spacing  is  great  enough 
so  that  crowding  will  not  result.  Rows  placed  at  the  ends  of  the  runs 
for  the  purpose  of  filling  in  open  spaces  are  called  spike  rows.  Some- 
times the  rows  tend  to  separate  near  the  middle  of  the  runs  and  then  a 
short  row,  or  fill  row,  is  used.  This  is  a  particularly  objectionable  row 
as  it  increases  irrigation  and  cultivation  difficulties. 


Fig.  11. — The  modified  basin  method  of  contour  irrigation. 


If  a  constant  grade  and  spacing  have  been  maintained  the  trees 
will  not  be  in  straight  rows  across  the  contour,  but  will  be  as  described 
under  type  1  (fig.  1).  By  using  a  hand  level  the  crossrows  can  be 
straightened  if  care  is  used  not  to  move  the  trees  too  far  off  grade 
so  as  to  cause  a  loss  of  grade  along  the  contour  row.  The  planting  will 
then  be  as  described  under  type  2  (fig.  2). 

If  a  surveying  instrument,  transit,  level,  or  hand  level  is  used 
the  same  initial  procedure  is  followed  as  for  the  grade  board.  The 
control  row  is  chained,  whereas  the  instrument  is  used  to  "run  in" 
the  grades.  On  large  tracts  of  fairly  uniform  topography  some  sur- 
veyors prefer  to  stake  out  every  fourth  row  and  then  give  propor- 
tionate distances  to  the  other  two  rows  with  the  chain.  This  method 
is  faster  but  should  be  used  only  on  uniform  topography. 


14 


CALIFORNIA    AGRICULTURAL    EXTENSION    SERVICE  [OlRC.  16 


A  third  method  used  by  surveyors  is  to  establish  a  control  row 
down  the  average  slope.  Guide  lines  at  the  top,  middle  and  bottom 
of  the  slope  are  then  run  at  right  angles  to  the  control  row.  On 
these  three  lines  markers  are  placed  at  the  same  distance  apart  that 
the  trees  are  to  be  placed  in  the  contour  rows.  With  these  markers 
as  a  guide  the  rodman  will  be  able  to  mark  the  tree  location  in  the 
contour  rows  when  the  levelman  tells  him  he  is  on  grade.  This  method 
produces  a  fine  type  of  planting  but  usually  results  in  a  fewer  number 
of  trees  to  the  acre  than  is  obtained  by  some  of  the  other  methods. 


Grade  of  furrow 
Duration  of  irrigation 
Depth   of  so/'/ 
Depth  of  wetting 
Laterai    spread 


27% 
46  rirs. 
£>7  in. 
27  in 
3.o~   ft 


Fig.  12. — Distribution  of  moisture  in  a  shallow  soil;  A,  contour  furrow  with 
a  grade  of  3.7  per  cent  and  with  a  cross  slope  of  27  per  cent;  B,  straight  furrow 
with  a  grade  of  27  per  cent,  but  with  no  cross  slope. 


CONTOUR   PLANTING   COSTS 

The  leveling  done  preparatory  to  contour  planting  is  little  more 
than  smoothing  the  soil  surface  and  in  many  cases  where  the  field  has 
been  previously  planted  to  field  crops  no  leveling  is  done. 

The  staking  costs,  where  the  work  is  done  by  the  use  of  a  grade 
board,  may  vary  from  $1  to  $5  an  acre,  depending  upon  the  topog- 
raphy of  the  land  and  the  experience  of  the  men  doing  the  work. 
Layouts  made  with  engineer's  equipment  as  a  rule  cost  more  than 
those  made  with  the  grade  board.  These  costs  range  from  $5  to  $15 
an  acre. 

IRRIGATION    PRACTICE 

The  irrigation  of  contour  orchards  requires  more  care  than  for 
straight  plantings  as  there  is  always  the  danger  of  the  water  breaking 
from  the  furrows  and  flowing  directly  down  the  slope.     Some  irri- 


1928]  IRRIGATION    OF    ORCHARDS    BY    CONTOUR    FURROWS  15 

gators  allow  grass  to  grow  between  every  other  pair  of  tree  rows  as 
a  protection  against  damage  from  broken  furrows.  Added  to  the 
above-mentioned  trouble  is  the  difficulty  of  taking  care  of  the  run-off 
from  the  stub  rows  and  in  getting  water  to  the  spike  and  fill  rows. 

The  number  of  furrows  used  to  the  tree  row  varies  from  one  to 
eight,  depending  upon  the  age  of  the  trees,  depth  of  soil  and  steepness 
of  cross  slope.  On  the  shallow  soils  on  steep  grades  the  water  tends 
to  move  laterally,  or  to  sub-irrigate,  so  fewer  furrows  are  used. 


Fig.  13. — Terraces  produced  by  plowing  in  one  direction  along  the  contour. 

A  modified  basin  method  of  irrigation  is  practiced  by  some 
orchardists.  In  orchards  that  have  become  partially  terraced,  either 
through  cultivation  or  leveling,  basins  are  made  on  the  upper  side  of 
the  tree  rows.  A  deep  furrow  is  made  on  the  upper  side  of  the  basin 
and  from  the  furrow  water  is  allowed  to  enter  the  basin.  Figure  11 
shows  the  method  in  use. 

The  efficiency  of  irrigation  on  steep  slopes  is  much  higher  with 
contour  planting  than  where  furrows  are  run  straight  down  the  hill. 
Figure  12  represents  the  distribution  of  moisture  in  an  Aiken  loam 
soil ;  first,  where  the  irrigating  is  being  done  by  running  water  down 
a  27  per  cent  grade  and,  secondly,  where  the  cross  slope  is  27  per  cent 
and  the  furrow  grade  is  3.7  per  cent.  The  data  are  from  experiments 
made  by  the  Division  of  Irrigation  Investigations  and  Practice. 


16  CALIFORNIA    AGRICULTURAL    EXTENSION    SERVICE  [OlRC.  16 


CULTURAL    PRACTICES 

Cultural  practice  in  contour  planting  varies,  but  as  a  rule  little 
cross  cultivation  is  done  on  the  steeper  slopes,  the  weeds  between  the 
trees  being  removed  by  hoeing.  Cultivation  along  the  contours  pro- 
duces terracing  unless  the  practice  is  to  plow  so  that  the  soil  is 
thrown  up  the  hill.  Figure  13  shows  the  terracing  produced  on  a 
contour  orchard.  If  the  cross  slope  had  been  greater  the  terracing 
would  have  been  more  marked.  Where  heavy  rains  occur  terracing 
is  verv  desirable  as  it  materially  reduces  erosion. 


12w-4'28 


